The pressure at which typical fluid distribution systems supply fluid may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of a gas regulator. Therefore, fluid regulators are implemented in these distribution systems in order to ensure that the delivered gas meets the requirements of the end-user facilities.
Fluid distribution systems can include a control system that has as a slam-shut device, which can operate based on a maximum downstream pressure, a minimum downstream pressure, or maximum and minimum downstream pressure. When the downstream pressure is at a normal operating value, the slam-shut device remains open. When downstream pressure varies beyond its set limits, the slam-shut device closes and prevents fluid from flowing through the fluid regulator. During an over pressure or under pressure situation of a downstream pipeline pressure, the slam-shut device is used as a secondary or tertiary protection device. However, in most applications, the slam-shut device has to be manually reset.
Current applications of non-venting over pressure protection utilize a monitor regulator or a slam shut. A monitor regulator is a normal pressure reducing regulator used in series with another pressure reducing regulator, the worker. If the worker regulator malfunctions and control pressure increases then the monitor takes over and maintains the control pressure at a slightly higher set point. Slam shuts are also used in series with the worker. If the control pressure climbs too high the slam shut will close cutting off all supply to the worker. A manual reset of the slam shut is required to reenergize the system.
Some applications want the functionality of both a monitor and a slam shut. When control pressure climbs too high the supply needs to be cut off but when the pressure drops to a safe level the device reopens.